In recent years there has been a sharp rise in interest and demand for more compact, light, energy efficient and economical voltage regulation solutions. In particular, tighter output voltage regulation, faster response times and lower volume are of major concern in the design of present-day voltage-regulator modules (VRM). For processing power from fractions of a watt to several tens of watts with fast transient performance, multi-stage interleaved converters combined with analog controllers have been predominantly used. There, fast response is usually achieved by designing a wide bandwidth control loop.
The advancement in hardware-efficient digital controllers enabled the implementation of advanced nonlinear control methods that improve the dynamic performance and, as a consequence, drastically reduce the size of the output capacitor. Among them, time-optimal control (TOC) and minimum-deviation controllers have demonstrated transient response with virtually the smallest possible voltage deviation, restricted only by the inductor's slew-rate. In VRM applications, this limitation has a major effect on the output voltage deviation for the case of an unloading transient event, primarily due to the high input-to-output conversion ratio. Another weakness of the classical time-optimal approach is the relatively higher current stress, beyond the steady-state value, that is required to restore the lost charge of the output capacitor during the recovery time. As a result, the overall power processing efficiency is impacted from consecutive transients, when compared to steady-state.
State-of-the-art solutions that exceed the performance of the time-optimal control method propose several circuit extensions to the original buck converter in order to increase the inductor's slew-rate. For example, extensions have been presented by addition of a fast auxiliary converter in parallel to the main converter with smaller inductance or with active region current injection circuit. However, it comes at the cost of an increased input filter since the load transient is reflected to the input. This is partly resolved by compensating only for half of the current mismatch, which does not increase transient time.
Recent studies have reported improved loading and unloading transient performance, obtained using an auxiliary converter connected to the output side [Z. Shan, S. C. Tan, and C. K. Tse, “Transient mitigation of dc-dc converters for high output current slew rate applications,” IEEE Trans. Power Electron., vol. 28, no. 5, pp. 2377-2388, May 2013.]. An independent energy bank is used, eliminating the impact on the input. However, this solution requires additional sensors to regulate the auxiliary operation and is limited by switching frequency to mid-range output voltages.
A recently-developed resonant switch-capacitor based gyrator converter (GRSCC) presented in [A. Cervera M. Evzelman, M. M. Peretz, and S. Ben-Yaakov, “A High Efficiency Resonant Switched Capacitor Converter with Continuous Conversion Ratio,” IEEE Trans. Power Electron, vol. 30, no. 3, pp. 1373-1382, March 2015] demonstrated an ultra-compact voltage regulator solution which obtains ideal transient response [A. Cervera, M. M. Peretz, “Resonant switched-capacitor voltage regulator with ideal transient response,” IEEE Transactions on Power Electronics, vol. 30, no. 9, pp. 4943-4951, September 2015]. However, a modest efficiency (around 85%) at steady-state is achieved due to high RMS currents. Nonetheless, its main advantage is that no magnetic element is required, allowing on-chip integration.
It is therefore an object of the present invention to introduce a new compact VRM solution that hybrids a buck converter with a resonant switched-capacitor auxiliary circuit that is connected at the load side to improve the response to transient effects in a minimum time and improved efficiency;
It is another object of the present invention to reduce the total volume of a voltage regulator module.
It is another object of the present invention to present a simple and cost effective solution by receiving an indication from the output voltage alone.